Excess-voltage arrester



Patented Jan. 16, 1951 EXCESS -VOLTAGE ARRESTER.

Sten Daniel Vigren, Stockholm-,-W-alter Otto Wilhelm Broberg,Nynashamn,.and.- Ernst Martin Thiele'rs, Stockholm, Sweden, .assignorsto, Telefonaktiebolaget L M Ericsson, Stockholm, Swe-- den, accompany ofSweden Application Septemberl; 1945, Serial No. 615,036 In Sweden April3, 1944 Section 1, Public Law-69 ;August8, 1946 Patent expires ,April.3,-196 4n.

1 Claim.

The invention relates to a modification of excess-voltage arresters,especially with regard to such ones, as are usedin large quantities inlow tension devices such as in telephone plants and in other low voltagedevices. An excess-voltage arrester which is very common in telephone devices is made of a spark gap withtwo electrodes, usually of=carbon,,said-electrodes being held at a short mutual distance, .for,instance by washers of insulating material, usuallymica. That type ofexcess-voltage arrester is described in the Swedish Patent No. 74,667,according to which electrodes and washers have received a suitable shapefor the function of the arrester, electrodes and washers havingfurthermore been assembled into a single unit by means of insulatingbinding means.

Of late ,it has been proposed to use, instead of the describedexcess-voltage arrester, voltagedependent resistances (siliceouscarbide, ocelit, etc.), which at normal operating voltages possess ahi'gh resistance, but underhigh voltages-show a very low resistance andthereby can dissipate the high-tension voltages.

Said arresters are mounted close to the part of the device whichis to beprotected, and are connected between the branches of an aerial line and.earth. The latest, researchers have however proved, thatinthunderstormsthe currentsin an aerial line (telephone line) can comeup to 1500 amperes or still more. That fact places especially greatdemands on a good earth connection for the arresters. If the earthconnection resistance comes up to 2 ohms, there will be, for saidcurrent, a tension of 3000 volts on the earth electrode, said tensionbeing hardly'supportable by the insulation in a telephone apparatus or atelephone wire of norm-a1 construction. The earth connection resistanceought thus preferably to be below 2 ohms. However, such a low earthconnection resistance cannot be obtained otherwise than at specialplaces, at any rate not without exceedingly heavy costs. Even an earthconnection resistance of ohms is difiicult to obtain.

The inventors have introduced a new way for connection of said excessvoltage arresters, which differs from hitherto known ways, thearresters, instead of being connected between line branches and earth,are according to the invention connected between the branches and themetallic body of the apparatus, which supports the inner details of theapparatus. Said body may as a result of lightning obtain a highpotential and the arresters are so provided, that the potentialdifhaving a great capacity to earth (water pipe,

central heating).

It is to be observed that with said arrangement the arresters will beless damasedby li htning than if they were directly connected to earth.

From another point of view-it is obviousthat it is not desirableto-touchthebody 0f theapparatus during thunderstormsit seems-to be of 4 minorimportance, as the subscribers are ordered not, to use; the telephoneduring thunderstormsit is however to be observed, that the same voltage?conditions must arise, if at-break down occurs on the body, whichduring'lightning is a normal defectof said apparatus. The invention ismoreover: intended fo telephone instruments with insulating casing, forinstance; of -molded plasticgmaterial, which surround the body of theapparatus and the inner details it supports,,so that thebody is thusnotnormally accessible from outside.

We think of the origin of atmospherical excesstension voltages,irrespective of direct downstrokes, more or less in the following way:In a static thunderfield, there arise charges on an aerial line (e. g. atelephone line with two branches). On changes of the thunderfield thesecharges are released and give birth to =a tension Wave on both sidesalong the telephone line. When said tension wave meets the parts of thedevice connected with the telephone line, break downs or flash-overs maytake place on earthed part or on apparatus metallic details, which havegreat earthing capacities or not very good insulation against earth,respectively. The beforementioned way of connecting an excess-voltagearrester, for instance a carbon lightning arrester, between each of thebranches and earth depends for its effectiveness on the supposition thatthe high-tension wave runs parallel to both branches, and that thereforeno potential diiierence worth mentioning exists between the branches. Inreality, however, the attenuation of the wave may often be differentwith regard to the two branches, and the charge of one of the branchesmay even for some reason be discharged in a larger or smaller degree.

With regard thereto the inventors have found another modification,wherein, besides said two arresters, there is also an arrester intendedto be connected between the branches. Said latter arrester is thensupposed to come into action should, for some reason, a potentialdiiference arise between the branches. Recent researchers have alsoproved that such a triple arrester obtains a higher protectingefficiency compared with previously known devices having only twoprotecting elements.

The described modifications will be more clearly illustrated by means ofthe figures in the accompanying drawing. Said figures refer moreparticularly to open spark gaps (carbon lightning arresters), but it isobvious that the principles of the invention may be applied with otherforms of excessvoltage arresters.

Fig. 1 shows the connection in principle. Two sparkor discharge gaps G1and G2 are connected in series to a telephone branch L1 and L2, and thepoint of contact between G1 and G2 is connected to the body A in atelephone apparatus. G3 is a spark gap connected right across thebranches, which in turn are connected to usual selecting equipment LF.

Fig. 2 shows a unit made of three interconnected carbon lightningarresters K1, K2 and The line branches are indicated by L1 and L2 andthe connection with the body of the telephone apparatus by B. Theelectrode blocks of the carbon lightning arresters are indicated at Eand the insulating washers at M.

Fig. 3 shows a unit made of only four electrode blocks (E), out of whichtwo (the central ones) have been provided with electrode surfaces onboth their sides.

The embodiments may vary in still other ways. The assembling into onesingle unit may be effected in different manners, by means of screens,springs or, most conveniently, by means of insulating binding means.

The arresters thus described may, when they are to be combined withtelephone devices, be placed in a suitable socket, eventually providedwith a cover, close to the telephone apparatus. An additional conductormust then be carried from the apparatus case to said socket.

A new way, by which said conductor may be dispensed with, is to mountthe arresters directly in the apparatus. Both ways may have theiradvantages, and the way of mounting may vary according to difierentcircumstances and with regard to different practical considerations.

The invenventors have introduced one more novelty, i. e. that the unit,with regard to its outer shape, is so composed, that it cannot beinstalled otherwise than in the correct cdnnecting way. This is anadvantage if the arrester is to be exchanged by a person unfamiliar withits construction.

We claim:

An excess voltage arrestor unit for equalizing the potentials intelephone apparatus components due to excessive voltages on line wiresconnected to said apparatus, comprising a plurality of more than twoexcess-voltage conducting layers, conductive electrode layersalternating with said excess-voltage conducting layers and supported incontact therewith to provide end and intermediate connection points forsaid unit, means for connecting intermediate electrode layers torespective wires of a telephone line, and means for connecting said endelectrode layers by a common connection to a metallic portion supportingat least one of said components.

STEN DANIEL VIGREN. WALTER OTTO VVILHELM BROBERG. ERNST MARTINTHIELLERS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 508,649 Thomson Nov. 14, 18931,303,383 Osborne May 13, 1919 1,573,068 Honaman Feb. 16, 1826 1,728,534Fortescue Sept. 17, 1929 1,750,090 Stanton Mar. 18, 1930 1,799,174 LoyeApr."7, 1931 2,053,988 Ferris Sept. 8, 1936 FOREIGN PATENTS NumberCountry Date 147,270 Switzerland May 31, 1931 251,292 Great Britain Apr,7, 1927

